to atheists or those who don't believe in a higher power

I just have a question: how do you not believe in any God or believe there isn't a higher power somewhere? Do you think we, animals & plants just randomly appeared? What about miracles? I'm just curious about your perspective on life in general. Personally i was raised to believe in Christianity, which I do to an extent. It's just hard for me to grasp the idea of no higher power? I'd love to be enlightened.